lkml.org 
[lkml]   [2011]   [May]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 4/9] ptrace: relocate set_current_state(TASK_TRACED) in ptrace_stop()
Hey, Oleg.

On Mon, May 16, 2011 at 01:57:11PM +0200, Oleg Nesterov wrote:
> > and helps future updates to group stop participation.
>
> OK, so I assume we need this change.

We don't necessarily need it but it makes things prettier later.

> But the comment looks a bit confusing to me. This is fine, I almost never
> read them ;) Just I'd like to ensure I din't miss something.

Oleg, IIRC, those comments were taken from your email pointing out
that set_current_state() needs to happen before clearing of TRAPPING,
so, if you're confused, I'm confused too. :-)

> > + * We're committing to trapping. TRACED should be visible before
> > + * TRAPPING is cleared
>
> This looks as if you explain the barrier in set_current_state(). And,
> btw, why can't we use __set_current_state() here ?
>
> And. not only TRACED, at least ->exit_code should be visible as well.

The racy part was task_is_stopped_or_traced() in task_stopped_code()
and the value of exit_code doesn't matter at that point. So, we need
at least smp_wmb() between __set_current_state() and clearing
TRAPPING.

> IOW. It is not that TRACED should be visible before jobctl &= ~JOBCTL_TRAPPING,
> we should correctly update the tracee before __wake_up_sync_key(), and I assume
> this is what the comment says.
>
> Correct?

All we need to update on the tracee is tracee->state and
~JOBCTL_TRAPPING and __wake_up_sync_key() can be considered single
operation. One doesn't make sense with the other. Anyways, if you
wanna update the comment, please go ahead.

Thanks.

--
tejun


\
 
 \ /
  Last update: 2011-05-16 15:19    [W:0.079 / U:1.352 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site